Welding torches of the water-cooled type used for TIG (tungsten inert gas), MIG (metallic inert gas) and plasma welding and cutting processes are typically connected to the power source (welding machine) with three or more lines. One line conveys cooling water to the torch head, a second line conveys the shielding gas to the torch head and the third line is used to transfer the electrical output from the power source or welding machine to the torch head. This third line also conveys cooling water back to the circulator reservoir. This third line is commonly referred to as the power cable. With plasma torches, there may be two power cables on each torch. These power cables are made from a flexible plastic tube or rubber hose that defines a conduit. Inside the conduit is a stranded copper cable formed of fine individual wires twisted or braided in a rope-like construction. The copper wires can be bare or plated. The copper cable functions as the electrical conductor for the power cable and is smaller in diameter than the inside bore of the conduit tube or hose so as to allow the cooling water to pass along side the cable, cooling the cable as the water passes thereover and is returned to the reservoir. To avoid any confusion in terminology, the term “cable” or “cable conductor” will be used herein to refer to the above-described current carrying stranded copper cable. The term “power cable assembly”, when used herein in connection with water-cooled welding torches refers to the cable and conduit combination which carries electric power to the torch and cooling water from the torch.
The copper cable in the power cable assembly rests on the surface of the inside bore of the conduit and is thus not entirely surrounded by water. This results in a less efficient cooling condition than would exist if the cable were completely surrounded by the flowing cooling water. As power cable assemblies are typically 12.5 to 25 feet in length, a substantial portion of the cable is in contact with the inside surface of the conduit and not with the cooling water. As a result of this relatively inefficient cooling of the cable, the cable must be relatively large in size to maintain the desired level of current capacity. The larger cable also adds bulk and weight to the power cable assembly and the welding torch resulting in less flexibility and added operator fatigue. A smaller cable size could be used if the cable could be more efficiently cooled by the water flowing within the conduit disposed about the cable.
During normal use of these torches, the torch head is continually being moved up and down and from side to side, as well as twisted, as the operator accesses the weld joint. This constant movement causes the fine copper wires of the cable to work harden and fracture. The problem is compounded by the fact that the cooling water passing over the copper causes hydrogen embrittlement. The hydrogen molecules from the water interact with the copper molecules embrittling the copper and causing the fine copper wires to splinter and break off. The wire splinters are carried by the cooling water flow to the end fitting on the power cable assembly where they collect and block the water flow through the fitting and cause overheating and torch failure. The use of other copper wire alloys that are less susceptible to hydrogen embrittlement, such as oxygen-free copper, has not resulted in appreciable improvement. It has been found, however, that when the twisted, braided or bunched copper wires are encapsulated with a thin coating of plastic, the current carrying capacity of the copper cable substantially improves. There is more arc stability at very low current levels and the fraying of the copper cable due to flexing and hydrogen embrittlement is eliminated. It has also been found that by utilizing a thin coating on the nature of about 0.010 of an inch, the coating has minimal insulating effect on the wire cable so as not to adversely impact the effectiveness and efficiency of the cooling water. While the individual copper wires will eventually break and fray due to normal work hardening of the copper, the plastic casing will contain the frayed splinters, preventing blockage at the end fitting. Providing the plastic casing with a suitably sized spline or star profile would tend to center the copper cable within the conduit such that the cooling water will completely surround the cable as it flows through the conduit, cooling the entire surface of the cable and greatly improving the water-cooling efficiency. As a result, a smaller diameter cable conductor can be used, reducing the weight and increasing the flexibility of the power cable assembly.
In air-cooled torch assemblies, the power cable again provides a dual function. Instead of conveying the cooling water back from the torch head to the circulator reservoir, the power cable used with air-cooled torches conveys an inert shielding gas such as argon to the torch head about the stranded cooper cable. Thus, when used herein in connection with air-cooled welding torches, the term “power cable assembly” refers to the cable and conduit combination which carries electric power and gas to the torch.
As the inert shielding gas in an air-cooled welding torch assembly flows from the supply tank through the power cable and out the end of the torch nozzle, the gas picks up heat from the copper cable, cooling the cable. While this cooling of the electrical cable by the flowing gas is not as efficient as the cooling effected by the flowing water in water-cooled torches, it does have a cooling effect. As with the water-cooled torches, the efficiency of this cooling effect is adversely affected by the contact between the cable and the inside bore of the outer tube or hose which prevents the gas from completely surrounding the cable as it flows thereby. Thus, the use of a thin plastic casing about the copper cable with a suitably sized spline or star profile to center the cable within the conduit will also improve the cooling efficiency of the electrical cable in air-cooled welding torch assemblies.
In addition to providing improved cooling in both water and air-cooled torches, the use of such a casing about the copper cable adds additional electrical insulation about the cable, inhibiting the grounding of the cable during use. High frequency current (“HF”) is often used to initiate and sometimes stabilize the welding arc. HF current travels on the surface of the copper cable and is prone to leak or go to ground anywhere along the cable as the cable lays on the floor or workbench. By centering the copper cable in the outer tube or hose of the power cable assembly, the tendency of the HF current to penetrate the outer tube or hose and go to ground would be further diminished in both water and air-cooled applications. Thus, the result of the present invention is a substantially improved power cable for use with both water and air-cooled TIG, MIG and plasma torches.